Industrial robot with automatic centering

ABSTRACT

The horizontal movement actuators 3 of an industrial robot arm 2 are deenergized after an initial engagement between a workpiece 8 grasped by a robot hand and a base member 10 disposed on a support table 12 so that any axial misalignment between the workpiece and a hole 11 in the base member is automatically corrected with the guidance of a chamfer 8a, 10b provided on the workpiece and/or the hole.

BACKGROUND OF THE INVENTION

The present invention relates to an industrial robot and, particularly,to such a robot which is capable of accurately fitting an assemblingmember into a corresponding hole formed in an assembling base fixedlysecured to a support structure to implement an assembly operation.

FIG. 1 is a front view of a hand of a conventional industrial robot forfitting a part to a base, in which an automatic alignment device 6 iscomposed of a upper plate 6a fixedly secured to a rotary shaft 5extending vertically from a free end of a robot arm 4, a core member 6bextending vertically from the upper plate 6a, a lower plate 6c arrangedin parallel to the upper plate 6a, and a link mechanism for movablysupporting the lower plate 6c in parallel to the upper plate 6a. Thelink mechanism is composed of three parallel links each having, atopposite ends thereof, spheres which are received in spherical bearings6d' and 6d"' provided correspondingly on a lower surface of the upperplate 6a and an upper surface of the lower plate 6c.

A cylinder member 6e is fixed to the lower plate 6c. Its length issufficient to extend over a lower portion of the core member 6b.

Such lower portion of the core member 6b is supported by an elasticmember 6f within the cylinder member 6e to allow a relative movementtherebetween. A gripper 7 is mounted on the lower plate 6c and hasgripping nails 7a actuated by an air or oil pressure motor to grip aworkpiece 8 in the form of a rod member having a chamfered end 8a whichis to be inserted into a blind hole 10a formed in a workpiece 10disposed fixedly on a table 9. The hole has a chamfered opening 10b.

When an elevation shaft of the robot is lowered to fit the rod member 8into the hole 10a with a center axis of the rod member 8 deviatingslightly from a center axis of the hole 10a, the fitting can be achievedas long as the mount of deviation is within the range of the chamfer 8aof the rod member 8, due to the deformation of the elastic member 6f asshown in FIG. 2. Therefore, under these conditions, by lowering theelevation shaft, the rod member 8 can be inserted automatically into thehole 10a and the desired assembling operation is achieved.

In the conventional hand device mentioned above, the manufacturing costis high due to such complicated mechanical structure, and the size ofthe hand cannot be reduced, resulting in a lowered space efficiency.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an industrial robothaving a compact hand while having an automatic alignment functionimplemented by deenergizing horizontal movement actuators of the gripperor hand when the workpiece reaches a predetermined position in relationto the hole.

With such features, the space efficiency is improved and a highlyaccuate fitting operation can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are front views of a conventional industrial robot,respectively;

FIG. 3 illustrates a general arrangement of an embodiment of the presentinventions;

FIG. 4 is a top view of the arrangement in FIG. 3;

FIG. 5 is a cross-section of a portion of the embodiment in FIG. 3,showing an actuator and a hand thereof in detail;

FIG. 6 is a block diagram showing the construction of a controllersection of the present invention;

FIG. 7 is a flow-chart showing a control operation of the robotaccording to the present invention; and

FIG. 8 is a front view of another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In an industrial robot according to the present invention, either an endportion of an assembly part grasped by a gripper of the robot or an edgeof a hole formed in an assembly base fixed on a support structure intowhich the part is to be inserted is chamfered, and the operation of anactuator for driving a robot arm holding the part is stopped to allow arelative horizontal movement between the part and the hole in which thepart is to be fitted when an initial engagement is establishedtherebetween by lowering the robot arm. The robot arm is then loweredfurther to complete the fitting operation.

In the present invention, since at least one of the pieces to be fittedtogether has a chamfered portion, a movable one of the pieces is allowedto freely move relative to the other fixed piece in a horizontal planeafter the initial engagement thereof is established, resulting in ahighly accurate fitting operation.

In FIGS. 3 and 4 which show a general arrangement of an embodiment of anindustrial robot according to the present invention in fornt and planviews, respectively, a main body 1 of a "pick and place" robot supportsa vertically movable elevation shaft 14 having an upper end supporting afirst actuator 3 operatively connected to one end of a first robot arm 2to swing it in a horizontal plane. A second actuator 3 is provided onthe other end of the first robot arm 2, and supports an end of a secondrobot arm 2 to swing it in a horizontal plane.

A third actuator 3 is provided on the other end of the second robot arm2, and drives a hand drive 7. The hand device 7 supports a workpiece 8which is, in this embodiment, to be fitted into a hole 11 formed in anassembly base 10 disposed on a base 12. Spare workpieces 8 are disposedon a parts table 13 arranged in the vicinity of the base 12.

The operation of the robot shown in FIG. 4 is controlled by a controllerC which is constructed as shown in the block diagram of FIG. 6. Thecontroller C is composed of a shaft control section 33, and I/O port 37,an information processing device 39 and a work position detector 35 forsupplying work position information through the I/O port to theprocessing device 39. The shaft control section 33 is operativelyconnected to the respective actuators 3 through the I/O port 37. Theprocessing device 39 includes a central processing unit 42, a read onlymemory 44 for storing a program, and a random access memory 40 forstoring various temporary data.

The operation of the robot is controlled according to the program storedin the ROM 44. Firstly, the elevation shaft 14 and then the actuators 3are actuated so that the hand 7 is positioned above one of theworkpieces 8 on the table 13. Then, the shaft 14 is lowered to allow thehand 7 to grasp the workpiece. Then, the shaft 14 and the actuators 3are drives so that the hand becomes positioned above a hole of the base10 as shown in FIG. 5, whereafter the shaft 14 is lowered until thechamfered ends 8a of the workpiece 8 enters into the chamfered edge 10bof the base 10 to a predetermined extent. When the chamfered end 8areaches the predetermined depth from the chamfered edge 10b of the hole,positioned information corresponding thereto is inputted by the workpositions information section 35 to the I/O port 37 as shown in FIG. 6.This information is processed together with information from the RAM 33and the ROM 44 by the CPU 42, and an instruction is supplied from theI/O port 37 to the control device 33 to deenergize all of the actuators3 so that the drive shaft 17 of the actuators become free from anyinfluence by the stators 15. All of the joints of the robot are thuspermitted to move freely with respect to their adjacent arms. Therefore,the hand 7 is put in a state where it can be moved by an externaldriving force.

Then, when the shaft 14 is further lowered, the chamfered end 8a of theworkpiece 8 is inserted into the hole of the base 10 with the guidanceof the chamfered edge 10b thereof. After the workpiece 8 is insertedinto the hole to a predetermined depth with centers thereof beingaligned, a programmed operation is performed.

FIG. 7 is a flow-chart showing the control operation of the robotmentioned above. As shown in FIG. 7, the hand 7 is firstly moved to aposition above the parts table 13 corresponding to the part 8. Then, thepart 8 is grasped by the grasping nails 7a of the hand. Thereafter, thehand 7 is moved just above the hole 11 of the base 10 by swinging therobot arms 2. Then, the part 8 is lowered by retracting the elevationshaft 14 to a first predetermined position, which is sensed by detectingthe amount of vertical movement of the shaft 14 or by detecting contactbetween the part 8 and the base 10. When it is sensed that the part 8reaches the first position, the stators 15 of the actuators 3 aredeenergized to render the hand 7 free of control. Under theseconditions, the elevation shaft 14 is lowered to further lower the part8 to a second predetermined position.

Then, the part 8 is separated from the hand and the stators 15 of theactuators 3 are energized to retrieve the robot arms. Thus, fitting ofthe part to the base is completed.

Although, in the mentioned embodiment, the vertical movement of the hand7 is controlled by the vertical movement of the elevation shaft 14, itis possible to fixedly provide an elevating device 18 having a shaft 19on a drive shaft of the third actuator 3 at the outer end of the secondarm 2 and to control the device 18 in the same way, as shown in FIG. 8.

As mentioned hereinbefore, according to the present invention, theactuators provide at various joints of the robot are deenergized torender the hand free from any restrictions due to the active actuatorsand to allow it to freely move in a horizontal plane when the initialpositioning of the hand is completed. The hand can be further movedhorizontally under the guidance of a chamfer formed in the workpieceheld by the hand and/or the hole of the base so that the completeengagement thereof is achieved. Therefore, there is no need of acomplicated automatic position regulator.

What is claimed is:
 1. An industrial robot for fitting in assembly part (8) held by a holding means (7) into a hole (11) of a base member (10) fixedly mounted on a support structure (12), comprising:(a) a robot arm (2) fixedly mounting said holding means on an end thereof, (b) elevation means including a vertical shaft (14;19) for vertically moving said holding means, (c) a plurality of actuators (3) for swinging said robot arm horizontally, and (d) control means for controlling operations of said elevation means and said actuators, (e) at least one base and an insertion end of said assembly part being chamfered (8a, 10b), said control means being responsive to a detection of said assembly part being lowered by said elevation means to a position near said hole of said base or to a position at which said part is inserted slightly into said hole to deenergize said actuators, and to cause said elevation means to further lower said part to thereby fit said part in said hole, the deenergization of the actuators rendering the holding means freely movable in a horizontal plane such that any axial misalignment between the assembly part and the hole is automatically corrected by a centering effect of the chamfer during the further lowering of the elevation means.
 2. The industrial robot as claimed in claim 1, wherein both said hole and said insertion end of said part are chambered.
 3. The industrial robot as claimed in claim 1, wherein said robot arm comprises a plurality of linked arms.
 4. The industrial robot as claimed in claim 3, wherein said actuators are individually disposed at linking portions of said arms.
 5. The industrial robot as claimed in claim 4, wherein said elevation means drives said holding means vertically via a coupling between said vertical shaft (14) and a rear end of said robot arm.
 6. The industrial robot as claimed in claim 4, wherein said elevation means comprises a cylinder (18) mounted on an outer end of said robot arm for vertically driving said shaft (14), said holding means being mounted on said shaft.
 7. The industrial robot as claimed in claim 1, wherein an actuator is provided in an outer end of said robot arm and said holding means is mounted on a drive shaft (17) of said actuator.
 8. The industrial robot as claimed in claim 1, wherein said control means detects an approach of said part to said base by monitoring the vertical movement of said elevation means.
 9. The industrial robot as claimed in claim 1, wherein said control means detects an initial insertion of said part into said hole by sensing contact between said part an said base. 